The 10 games have a greater than normal impact on your MMR, which is what actually determines your rank (as opposed to simply wins/losses). If your MMR is sufficiently bad that the big MMR boost that 10-0 placements nets you still leaves you in bronze, then you would certainly have been placed in bronze without the placement matches. The difference though is with the increased MMR gains on the placement matches, your MMR might be such that you 'only' need to play 100 matches to climb to silver, while in a placement-less system where MMR gains/losses were normal throughout it might be a full 200 matches.
Keep in mind that although there is a soft reset to MMR at the start of season (which pulls most players downwards), your end of pre-season MMR is still a factor, so a top tier challenger god going 10-0 would place plat 1, while someone who spent all preseason trolling could conceivably have an MMR so low that 10-0 still placed them bronze 5.